Flat panel field emission displays (FEDs), like standard cathode ray tube (CRT) displays, generate light by impinging high energy electrons on a picture element (pixel) of a phosphor screen. The excited phosphor then converts the electron energy into visible light. However, unlike conventional CRT displays which use a single or in some cases three electron beams to scan across the phosphor screen in a raster pattern, FEDs use stationary electron beams for each color element of each pixel. This allows the distance from the electron source to the screen to be very small compared to the distance required for the scanning electron beams of the conventional CRTs. In addition, the vacuum tube of the FED can be made of glass much thinner than that of conventional CRTs. Moreover, FEDs consume far less power than CRTs. These factors make FEDs ideal for portable electronic products such as laptop computers, pocket-TVs and portable electronic games.
As mentioned, FEDs and conventional CRT displays differ in the way the image is scanned. Conventional CRT displays generate images by scanning an electron beam across the phosphor screen in a raster pattern. As the electron beam scans along the row (horizontal) direction, its intensity is adjusted according to the desired brightness of each pixel of the row. After a row of pixel is scanned, the electron beam steps down and scans the next row with its intensity modulated according to the desired brightness of that row. In marked contrast, FEDs generate images according to a "matrix" addressing scheme. Each electron beam of the FED is formed at the intersection of individual rows and columns of the display. Rows are updated sequentially. A single row electrode is activated alone with all the columns active, and the voltage applied to each column determines the strength of the electron beam formed at the intersection of that row and column. Then, the next row is subsequently activated and new brightness information is set again on each of the columns. When all the rows have been updated, a new frame is displayed.
Beside the difference in image scanning methodology, a more significant difference between FEDs and conventional CRT displays is that conventional CRT displays emit electrons with "hot" cathodes, while FEDs utilize "cold" cathodes. For instance, in a conventional CRT display, a metal composite is heated to about 1200.degree. C. to emit electrons. These electrons are then focused into a tight beam and accelerated towards the phosphor screen. In contrast, FEDs generate a high electric field by applying a voltage across a very narrow gap between emitter-tips and emitter-gates to emit electrons. Because it is not necessary to expend thermal energy to emit electrons, "cold" cathodes consume far less power than "hot" cathodes.
One drawback of the "cold" cathodes, however, is that emission efficiency of the electron emitters is moderately unstable. The electron emitters may degrade after several hours of continuous operation, resulting in a lower emission current and a dimmer display. Some electron emitters may degrade faster than others, resulting in a display having uneven luminance across the screen. Naturally, these visual artifacts are highly undesirable for a high-quality flat panel display.
Therefore, what is needed is a system for and method of extending the operational life of FEDs. What is further needed is a system for and method of extending the operational life of FEDs that can be implemented without redesigning the entire FED screen and remain cost-effective.